Historically, the Mercantile Library had several bound volumes of "Baptist Pamphlets" which were initially part of John Mason Peck's library but catalogued together under one call number. These volumes have been disbound and each pamphlet put in a separate, non-acidic enclosure. A number has been added to an alphabetical arrangement. The list is roughly arranged alphabetically by the first important word of the Church, benevolent Society, or other organization's title or name concerned.

The Saint Louis Lyceum was a public forum for lectures and debates in early St. Louis. It was founded in 1838 in the spirit of the Lyceum Movement, a national effort towards self-improvement and community led education for adults. It maintained and built upon the library of the city's first subscription library, the St. Louis Library Association, which was founded in the early 1820s. The Lyceum overlapped in activities and collections with the Young Men's Lyceum and the Mechanics' Institute of St. Louis. The archives and books of these early libraries were bought by the Mercantile Library in the early 1850s, and became a cornerstone bibliographic collection at the Mercantile. This collection was reassembled from the stacks of the Mercantile through study of the original accession records concerning the acquisition in 1851.
The larger collection consists of approximately 500 printed books and pamphlets from this early book collection, some with association annotations, original ownership marks, or bookplates. Most of the scanned materials relate to the week to week meeting minutes, circulation records, and founding documents.